This invention relates to hermetic rotary compressors for compressing a compressible gas such as a refrigerant. In particular this invention relates to an improvement in such compressors whereby a biasing force is applied to the suction side of the compressor sliding vane to offset lateral forces on the vane extension generated by the pressure differential in the compression chamber.
Hermetic compressors of the type to which this invention relates and which are used in appliances such as refrigerators, freezers, air-conditioners and the like, generally include a hermetic casing or housing, a compressor cylinder block and an electric drive motor for operating the compressor. The compressor cylinder block includes an axial bore in which is disposed a roller member disposed about an eccentric portion of the crankshaft. The crankshaft may be journalled in one or more bearings such as a main bearing and an outboard bearing. The compressor bearings generally also serve as end plates for the cylinder whereby the bore is formed into a compression chamber within which the roller member revolves. The compressor cylinder also includes an axial slot within which a reciprocable vane is slidably disposed, the end portion of the vane engaging the periphery of the roller to divide the chamber into a high pressure or discharge side and a low pressure or suction side.
In operation, gas is drawn into the suction side of the compression chamber wherein it is compressed and then discharged through a discharge port disposed between the high pressure side of the compressor chamber and the compressor housing. During the operation of such a compressor, especially compressors of relatively large displacement, a considerable side or lateral force is exerted on the vane or, more specifically on the portion of the vane which extends into the compression chamber. These forces result from the high discharge pressure on one face of the vane and the suction pressure on the other face of the vane. This lateral force is transmitted by the vane to the vane slot walls and especially to the cylinder edge of the vane slot wall on the suction side of the vane. The result is a concentration of vane slot wear in that area as well as wear of the vane. It is therefore desired to provide for the reduction of such lateral forces and the attendant vane and vane slot wear. Additionally, due to the exacting tolerances to which the parts of the compressor must be machined, it is desired to provide proper lubrication for the vane to reduce wear and friction forces and thereby extend the life of the compressor.
Numerous arrangements have been provided in the prior art for lubrication of compressor vanes. One such arrangement is disclosed in U.S. patent application Ser. No. 670,307, filed Nov. 13, 1984 and assigned to the assignee of record of the instant application. In this arrangement two grooves are provided respectively in the opposed side walls of the cylinder vane slot. These grooves are connected to an axial bore in the crankshaft by means of a connecting passage in the outboard bearing. The bottom end portion of the crankshaft is provided with an oil pump which is disposed in an oil sump. Oil is drawn upwardly into the crankshaft and is pumped outwardly through the connecting passage into the vane slot grooves. By means of this arrangement a supply of oil under positive pressure is at all times provided to the compressor vane for lubrication thereof. However, since the pressure of the oil in the vane slot grooves is equal on both sides of the vane the forces on the vane generated thereby will cancel each other. The lateral force generated on the vane due to the difference in pressure between the suction and discharge sides of the compressor chamber is therefore not offset by this lubrication arrangement.
Another prior art patent disclosing a lubrication arrangement for a compressor is U.S. Pat. No. 2,883,101. This patent discloses a groove in the compressor vane rather than the vane slot. Oil is pumped upwardly from an oil sump to a point above the compressor cylinder from which it runs downwardly by gravity through an opening in the side of the vane slot and from thence into the vane groove. The vane, as it reciprocates, will deliver oil into the compression chamber by means of the vane groove. This arrangement therefore does not supply oil to the vane groove under positive pressure and does not provide a bias force for offsetting lateral forces on the vane.
U.S. Pat. No. 3,513,476 discloses recognition of the lateral force due to the pressure differential between the high and low pressure gas to which the vane is subjected and the attendant wear of the vane and vane slot. The solution provided for solving this problem is to provide two vane slot grooves, one on each side of the vane, and to asymmetrically offset these grooves with respect to a line which extends perpendicularly to the longitudinal axis of the blade. The groove on the discharge side of the vane is moved toward the bore and the slot on suction side of the vane is moved away from the bore. Oil is provided to the grooves by means of a helical groove in the outer surface of the crankshaft from which the oil flows by gravity over a raised ridge into a perforation and from there into the oil grooves.
Yet another prior art patent disclosing recognition of the lateral pressures on a sliding compressor vane is U.S. Pat. No. 3,813,193. In this patent the solution proposed is to provide four grooves in the vane slot and to connect these grooves respectively to areas of high pressure gas and low pressure gas to balance the lateral forces exerted on the vane.
None of these prior art solutions are completely satisfactory in solving the problem of unbalanced lateral forces on the vane while simultaneously providing lubrication for the vane. What is therefore desired is to provide a very simple, low cost, yet effective solution. It is also desired to provide a biasing force on the suction side of the compressor vane while at the same time lubricating the vane. It is furthermore desired to generate such a biasing force which is relatively constant.